The removal of metal ions from aqueous solutions is a process common to many manufacturing environments. For example, it may be desirable to remove metal ions from water supplies entering a manufacturing site if a manufacturing process is sensitive to those ions. Likewise, metal ions may be removed from effluent leaving the manufacturing site in order to recycle the metal or to mitigate the effect of the effluent on downstream treatment systems or the environment. In this case, the removal of metal ions may not need to eliminate all traces of them, but merely remove them to the degree that their remaining levels are below the regulatory limit.
A common system for removing metal ions from aqueous solutions involves the use of ion exchange resins, wherein the metal ion-containing aqueous solution is brought into contact with the ion exchange resin. As the name suggests, ion exchange resins work by exchanging one ion for another, causing metal ions to become bound to the ion exchange resin while releasing different ions.
For example, a typical ion exchange resin will exchange positively charged sodium ions (sodium cations) for other metal cations carried in the aqueous solution, resulting in the binding and removal of the metal cations but adding sodium ions to the aqueous solution. The ion exchange resin must be periodically regenerated to remove the accumulated metal cations or else its effectiveness will be diminished. It may be necessary to remove the resin from the system in order to regenerate it. Additionally, strong acids or other chemicals may be required to regenerate the resin, which may introduce new remediation challenges.